Have been seeing high dust counts at End-Y during evening ops shift. The counts are not that far off the normal values for End-Y, but there is no apparent cause for the spikes. Will continue to monitor.  

Darkhan, Jenne, Stefan, Evan

Upon revisiting the shape of the DARM loop, we found that we had 4 dB of gain peaking from 10 Hz to 50 Hz.

That seems a bit too strong for our taste, so we took a look at the DARM suscomp filter that we've been using for the past few months. Aside from the low-frequency (<2 Hz) suspension resonance compensation and the high-frequency (>900 Hz) inversion rolloff, there is a single pole at 200 Hz.

This serves us well when locking DIFF, but in full, low-noise lock it costs us phase (not least because we also have the effect of the 350 Hz RSE pole).

Anyway, there is now a filter installed in EY L3 lock with a zero at 200 Hz and a pole at 1000 Hz in order to push this pole up to higher frequency. This gives us a modest improvement in phase margin at the DARM ugf (34° to 46°). The DARM ugf is 40 Hz or so (more or less the same as before). The EY ESD has about 16000 ct rms, mostly accumulated around 1 kHz (magenta/orange in the attached spectra show the before/after).

[In the longer term, we should just roll p/z pair into the suscomp filter, so that it rises like f essentially from 1 Hz to 1 kHz. Then put a 200 Hz pole / 1000 Hz zero pair in EX L3 lock, so as not to disturb the DIFF loop shape. However, I've put what we have so far into the guardian and it works fine.]

Darkhan and I retuned the DARM OLTF template in order to not saturate with this new loop shape. The attachment shows the before (blue) and after (red), along with the closed-loop gain and loop suppression. There's still moderate gain peaking below 20 Hz.

Evan, Stefan,

Evan will make a more detailed log entry with actual measurements, but here are the highlights:
- We beat the 45Mhz signal from the installed and the spare harmonic generators.
- the first odd thing was that straight out of the harmonic generators, the 45Mhz signals were out of phase by about 170deg, even though the 9MHz inputs were nicely in phase...
- We phased the two signals to be exactly in phase an stuck them into a mixer: 0.415V
- We phased the. To be exactly 90deg apart: no DC signal, and ~ 220nV/rtHz of flat  broadband noise.
- this gives 5.3e-7 rad/rtHz between the two signals.
- Assuming equal and non-coherent contributions, the phase noise of one box is thus: 3.75e-7 rad/rtHz
- If we assume that the oscillator phase noise has the same coupling as the oscillator amplitude noise (9e-2mA/RIN), we would expect 3.4e-8mA/rtHz. Thats's pretty close to what we see on ODC_DCPD_SUM.

We had noticed last week that the refl 45 WFS were phased incorrectly, and tonight Jenne and I rephased them by moving PR3 100 counts in pitch.  This only affects the PRC2 loop.  We've locked and engaged the ASC several times since then, and this seems fine.  

While we did improve the phasing and tuned it to within 5 degrees, I is only about 9 dB higher than Q for PR3 motion.  We will need a different phasing strategy, where we phase 45 to minimize the signal from chard in one quadrature if we want to distinguish between PR3 motion and CHARD.

The first two attached screenshots are the phases before we started, except that for REFL A the phase of the first quadrant was -165 not -145.  The following 2 screenshots were the phases we rephased.  For the time being we have reverted. 

Jenne and I spent some time making SDF green before the enigneering run starts in the morning.  

The main things that are still showing diffs are HAM1 HPI, some violin mode damping settings on ITMY, and many diffs in CALCS.  

While we were doing this we noticed a potentially nasty trick that SDF does.  We chose some channels that should be not monitored from the list of DIFFs, and right as I was about to CONFIRM, the IFO lost lock.  A new diff showed up on the top of the list, and the channels I had intended to not mon were moved down the list, but the yellow squares stayed in the same place.  It would have been verry easy to miss this and apply the action to the wrong channels.  Jenne is putting this in bugzilla.  

The OMC_LOCK guardian now has the states ADD_WHITENING and REMOVE_WHITENING, which do what they say on the tin. If you have one stage of whitening on, running ADD_WHITENING will turn on one more stage, etc.

They are not connected to the rest of the graph at all, so you'll have to run them manually.

They are intended to be compatible with full lock, so they can be run at any time (so long as you don't end up saturating the DCPD ADCs, of course).

ALL TIMES IN UTC

Arrived to find IFO beginning lock sequence after TJ did some PRMI alignment to help DRMI. It seems previous lock segments were on the average of about half a hour

• 23:09 DRMI locked.

• 23:10 Robert in the LVEA

• 23:15 Guardian hung on an OMC error. (no light on QPD)

• 23:37 noticed HEPI L4 WD SATURATION MONITOR for ITMX is at 43820cts. WD limit is set to 30000(safe)(max is 122880). WIll reset at next opportunity.

• 23:29 Dick and Wayne in the optics lab

• 23:30 Robert out of the LVEA

• 23:48 reset ITMX HEPI WD accumulator.

• 00:10 DRMI taking in excess of 16 minutes. No environmental noise observed. Tried PRMI lost lock. restored slider values back 1 hour. Re-Aligned SRM DRMI locked 1 minute later.

• 00:29 Wayne out of optics lab.

• 01:02 Stefan out to CER

• 01:16 Dick out

• -1:20 Guardian ISC_LOCK in Error at Engage ASC Part 2. Stefan cleared error

LOCK LOG:

• 23:23 Locked at NLN

  • 23:47 Lockloss at ENGAGE_ISS_SECOND_LOOP

    • DRMI ~ 13 minutes to lock

• 23:49 Began sequence

  • DRMI taking over 16 minutes.

  • 00:20 PRMI align

• 00:48 Locked at NOMINAL_LOW_NOISE

  • 0:48 Lockloss . Gabriele trying to fine tune OMC

• 00:49 Began Sequence

  • 01:07 Lockloss @ ENGAGE_ASC_PART3

• 01:08 Began Sequence

• 01:29 Locked at NOMINAL_LOW_NOISE

• 00:00 IFO still locked. 70mpc

Evening Summary:

• IFO locking in half hour segments. DRMI was taking a rather long time locking. Visiting PRMI may have improved it slightly.

• Stefan and Evan have been taking measurements and tuning for the last 5.5 hour lock.

• IFO still locked at shift change @ ~70-72mpc.

The inspiral range had trended down significantly in the last ~2h of the lock.

- Looking back at the data the spectrum showed a 1/f^2 noise floor between 15 and 150Hz. (plot 1)
- This floor was clearly generated by frequent glitches. Plot 2 shows a filtered time series for the bad time (blue, 2015/08/16 15:05 UTC) and a good time (red, 2015/08/16 13:35 UTC)
  Filter: zpk([0;0;],[1000;1000],1,"n")ellip("BandPass",6,1,80,30,200)

- Sheila noticed that both the M2 and M3 coils of the SRM were hovering around the ominous 65536cts mark, so there is the suspicion that these are SRM glitches. However I couldn't line them up convincingly... Either way, Sheila did the top stage bleed-off today, so we will see...

Evan, Sheila, Jenne, Stefan

we have been intending to offload the SRM length control to M1 (instead of M2) for some time now.  This is now done in the guardian, and is basically a copy of what was done in alog 19850.  The only difference is a 50Hz Cheby low pass, which is used as a cut off instead of a 70 Hz elliptic.  This is in the ISC_DRMI guardian now. 

I have turned off the L2P and L2Y decoupling, as I could only use very low gain with them on.  

Update:

Neither the PRM nor SRM had a true integrator in the top stage, now they both have one which we have engaged by hand, and the guardian has been edited to turn these on, which we will test after our next lockloss. 

Last update: We've tested the integrator switching on now, its fine.

Sheila, Evan

Running the dc-coupled oplev servo on SR3 for long periods of time seems to be causing us grief (LHO#20519).

As an alternative, we are trying out a cage servo which feeds the witness sensor in pitch back to M2:

ezcaservo -r H1:SUS-SR3_M3_WIT_PMON -g -300 -s <SR3 M3 P witness setpoint> H1:SUS-SR3_M2_TEST_P_OFFSET

The step response of this loop has a time constant of 30 s or so.

Arrived with the IFO in Nominal Low Noise for 12+ hours.

Two things were a bit odd though: The ISS second loop was not engaged, and I didnt see an alog about that being done on purpose. Second, the the Inspiral range has been dropping from 70Mpc for about an hour since I arrived. We are down to about 40Mpc at 15:19 UTC. I'm trying to find a cause and I will log if I find anything.

Log in UTC:

1539 Robert making noise injections.

1547 Lockloss

1608 Robert to LVEA

1624 Robert out

1657 Started Initial Alignment

Lost lock at 1547 UTC after 12+ hours. The alignment looked pretty bad afterward and I couldn't even get PRMI to lock. So, at 1657 I went to do an initial alignment. This seemed to make things much worse. I ended up moving PR2, PRM, and SRM quite a bit before I started seeing some activity on POP90 and POP18. This finally got PRMI and then DRMI.

Now it keeps losing lock at ENGAGE_ASC_PART1 when the CHARD Y gain is set to -2. I've tried -1, that didn't work. I will keep fiddling and see what I can get to work.

I noticed that it has been sending several thousands of counts to the actuators. The modes are well damped so I changed the gain to 0 for now. I have reduced the gain of this filter in Guardian to be 100 but I have not reload the code becase I don't want to risk causing a lock loss tonight (I'm not sure if reloading the code will cause any glitches in the control signal).

I made the suggestion before, but today I actually tried it:

By driving both L2 and L3 at a fixed frequency, but with a gain and phase such that their contribution cancelers in DARM, we can easily monitor (and servo, if we want) the ESD drive strength, which is expected to vary with charging.

This method has the big advantage that there are NO LARGE cal line resulting in DARM.

Here are the settings I tried:
- H1:SUS-ETMY_L2_TEST_L_EXC: drive with 300 cts at 20Hz, phase   0  deg
- H1:SUS-ETMY_L3_TEST_L_EXC: drive with 51.7cts at 20Hz, phase 134.2deg

The resulting line in DARM is only ~0.016 times the size of the line with only 1 drive. I also used the H1:SUS-ETMY_L2_DAMP_MODE7_BL filter bank to monitor the line strength. This suggests we should get on the order of 1% monitoring precision on a few second time scale - all while only producing the tiniest peak in DARM - with no up-conversion feet.

Also - since the biggest variation we see is on the microseism time scale - we should try the ESD linearization..

I alrady noticed yesterday that the DARM noise at the periscope peaks (200-400 Hz) was high at the beginning of the lock and then reduced over time.

The first attached plot shows a BLRMS of DARM around those peaks, starting right after reaching the low noise state. There is a clear reduction of the noise over time. The second plot shows that on a similar time scale, the OMC alignment output signal changed, mostly ANG_Y.

This seems to confirm the idea that input beam jitter at the periscope peaks is converted into intensity noise by an OMC misalignment, which changes over time.

To confirm this, I move the OMC angular loops during full lock, adding offsets of few tens of counts to the POS and ANG loops. The third plot shows the steps in the control signals. I was able to reduce the BLRMS by adding an offset of -40 to the ANG_Y loop. The fourth plot compares the DARM spectrum with (red) and without (blue) the ANG_Y offset. I should have increased the offset more. Unfortunately, I noticed that the output was hitting the limit of 300 and I stupidly increased it to 1000: but since the loop was integrating, I broke the lock since I suddenly increased the output from -300 to -1000.

However, the experiment confirms that the noise at the periscope peaks changes in amplitude with the OMC alignment, which is not optimal.

J. Kissel, J. Driggers, C. Cahillane, K. Izumi

I've taken the data that we took last Sunday of the ALS DIFF PLL Open Loop Gain TF and Boosts (from LHO aLOG 20363), built a model of the loop. Given the precision of the measurement, I can make a model the reporoduces the boost filters and the PLL OLGTF to within 1% and 1 [deg]. The most important outcome of this is the ability to characterize the frequency dependence of the low-pass filter just before the VCO. The nominally z:p = 40:1.6 VCO Filter is actually a z:p = 1.05:40 Hz filter. This means that, in using the ALS DILL PLL CTRL signal, prior estimates of overall actuation strength of the QUADs (i.e. LHO aLOH 18711) was over estimated by (1.6-1.05)/1.6 = 34%. This potentially explains some of the discrepancy we saw when comparing the three methos, PCAL, Free Swinging Michelson, and ALS DIFF VCO in LHO aLOG 18767.

Of course, as you know, we plan remeasure all methods and make the comparison again.

Details:
------------------------------------
Here're the final answer numbers of the model:
                                                   Traditionally Quoted "Nominal" Values            This Model's Fit Values
Phase Frequency Discriminator (PFD)                        z:p = (none):(0Hz)                   z:p = (none):(0Hz, 450kHz)
Voltage Contolled Oscillator (VCO)                         z:p = 40Hz:1.6Hz                     z:p = 40Hz:1.05Hz
Phase Locking Loop (PLL) Control Common Gain               26 [dB]                                                     25.5 [dB]
Phase Locking Loop (PLL) Control Boost Filter 1            z:p:k = 20kHz:2kHz:0dB               z:p:k = 1.9kHz:1.89kHz:0dB
Phase Locking Loop (PLL) Control Boost Filter 2            z:p:k = 2kHz:40Hz:0dB                z:p:k = 1.95kHz:38.55Hz:-0.2dB

------
Attached are figures demonstrating the progression and precision of the model.
pg1 : The final answer, showing the model of the ALS DIFF PLL Open Loop Gain TF from 0.1 Hz to 1e6 Hz.
pg2 : PLL Control Boost Filter 1; a comparison between measurement, model with fit parameters, and nominal parameters
pg3 : PLL Control Boost Filter 2; a comparison between measurement, model with fit parameters, and nominal parameters
pg4 : PLL OLGTF, with out the boosts engaged
pg5 : PLL OLGTF, with boosts engaged
pg6 : A comparison between fit residuals and nominal residuals with measurement.
pg7 : A confirmation that the closed loop gain, G / 1+G, of the ALS DIFF PLL is indeed 1.0 to better than 0.1% out to 1 kHz.

------
Perhaps it is of interest for the scrutinous to focus on pg 6, where I compare the residuals, and it'll illustrate my motivations for the fit paramaters, and my quoting that we trust their values to such high precision.
Question 1: Why d'you think the magnitude uncertainty is less that 1%, when clearly the boost OLG measurement residual falls by 15% with frequency below 1 kHz, and the unboosted measurement residual falls by 10% with frequency below 100 Hz?
     Recall that at these frequencies, below 1 kHz and 100 Hz for the boosted and unboosted measurements, respectively there is a rediculous amount of loop suppression. As such, given that the phase residual holds up well to fitted poles, and has little affect on the magnitude residual, I suspect that the measurement magnitude drops with frequency as the suppression increases due to very-small, non-linear, in-loop voltage affects.

Question 2: Why do you think there's an 450 kHz pole in the PFD when you've only measured up to 100 kHz?
     I played around with the very-high-frequency response for a while. Of course, a pole is the only high-frequency tool one has to affect the magnitude residual, and 450 kHz was a good balance between the fitted time delay, and the frequency of the pole. Both the 800 [ns] and 450 kHz pole are "plausible." Inside the PFD, there is a fast chip, that the data sheet claims is good up to 100 kHz, but that doesn't mean much, because you don't know what rolloff filter was chosen. 800 [ns] would correspond to a few hundred meters of cable length difference, so it's not that. But if I see a consistent ~230 [ns] delay in the indepednent measurements of the boost filters, it's not crazy to think that the whole phase-locking-loop accrues 800 [ns].

------
The analysis script that built this model is commited to the CAL SVN here:
/ligo/svncommon/CalSVN/aligocalibration/trunk/Runs/PreER8/H1/Scripts/ALSDIFF/ALSDIFFModel_PreER8.m
and the plots live here:
/ligo/svncommon/CalSVN/aligocalibration/trunk/Runs/PreER8/H1/Results/ALSDIFF/2015-08-09_H1ALSDIFF_PLL*.pdf